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采用透射电镜观察了铁镍(Fe32%Ni)合金在形变温度500 ℃(＜05Tm)、形变速率10-2 s-1的变形条件下多轴锻造变形过程中的微观结构演变。结果表明，低温多轴锻造强变形可明显细化晶粒，细化过程为：首先，位错墙、位错缠绕等结构通过大量位错滑移运动在原始晶粒内形成；其次，不同方向的变形导致不同方向的滑移系开动，从而致使不同方向的位错墙互相交叉，将原始粗晶粒细分成小尺寸的胞块结构，当变形量达到一定程度时，位错墙和位错缠绕结构内的位错开始重新排列，形成小角度晶界，导致亚晶粒形成；由于变形量不断增加强迫大量的位错在亚晶界处积聚、重排，同时不同方向的变形造成亚晶发生转动，位错重新规则排列及亚晶转动使小角度的亚晶界转变为大角度晶界，从而形成细小的新晶粒。

The microstructure evolution of Fe32%Ni alloy multiaxially forged at the temperature of 500 ℃ (＜05Tm) and strain rate of 10-2 s-1 was investigated by using TEM. The results show that the grains were obviously refined by low temperature multiaxial forging, and the grain refinement mechanism was presented: firstly, the dislocation walls and dislocation tangles were formed in the original grains by large amounts of dislocation glide; then the glide system with different direction were activated by different direction compression, which resulted in the formation of dislocation walls and dislocation tangles in different direction. These dislocation walls and dislocation tangles subdivided the original grains into fine cell structures. The dislocations in the dislocation cell boundaries will be rearranged when the cumulative strain reached some certain amount, then the subgains were formed. The increased strain makes large amounts of dislocations rearrange in the subgain boundaries, and at the same time the rotation of subgrains is caused by the deformation in different direction. The dislocation rearrangement and the rotation of subgrains resulted in the changing of low angle subgian boundaries into ordinary high angle grain boundaries, which resulted in the formation of new fine grains.